Capillary fill test devices have been manufactured and used in a wide variety of fluid testing applications in the laboratory, in the clinic, in the field and in the home. Such devices allow a rapid, convenient, and dependable analysis using very small sample volumes of test fluids. Capillary fill devices have found wide use particularly in the analysis of blood and other biological fluids.
Generally capillary fill test devices are constructed to have a test fluid receiving structure including a fluid loading port or sample well, a vented fluid test volume for containing the portion of the test fluid from which data characterizing a chemical or physical property of the fluid is collected, and a capillary flow-through conduit for transporting the fluid sample from the fluid receiving structure to the test volume. The capillary conduit includes a capillary aperture communicating with the fluid receiving structure so that when a fluid is delivered to that structure in contact with the capillary aperture, it is drawn through the conduit and into the vented test volume by capillary action. The capillary conduit and the test volume elements of the capillary fill test device are sized to provide consistent analyses and dependable accuracy with a minimum volume of test fluid. In some devices the conduit and the test volume each have the same flow through cross-sectional area and thus appear as a unitary capillary volume. In other devices the conduit portion is visibly distinguishable from the test volume appearing in plan view as a narrowed passageway in the device having a flow through cross-sectional area less than that of the test volume. The test volume typically includes additional components that interact with the fluid (or components of the fluid) delivered to the test volume to provide a photometrically, electrometrically, acoustically or mechanically detectable indication of a physical or chemical property of the fluid.
Capillary fill test devices are generally used in combination with a second device, most typically an electronic instrument designed to detect the existence or the extent of a predetermined interaction of the fluid sample, or one or more analytes in the fluid sample, with one or more other components of the capillary fill device in the test volume, for example, an electrode structure and/or one or more fluid-interactive or analyte-reactive compositions. The electronic instrument is used to assess the sample fluid in the test volume of the device, most typically by photometric or electrometric techniques after a predetermined sample reaction period.
Capillary fill devices are often designed to be positioned in the electronic instrument before the device is loaded with the fluid sample. When the capillary fill device is properly positioned in the instrument, the fluid receiving portion is external to the instrument and accessible to the user, and the test volume is located in electrical or phototransmissive/photoreflective communication with a sensor element capable of detecting and reporting a condition or change of condition of the fluid in the test volume after or during a predetermined time period. A volume of test fluid is then delivered to the fluid receiving structure to contact the capillary aperture of the capillary flow conduit so that it is drawn by capillary action into and through the conduit and into the vented test volume. The instrument can be equipped with sensors to detect the flow of the test fluid through the capillary flow conduit and into the test volume; optionally the instrument can be designed to use such detected flow to initiate a test sequence. In some fluid testing applications, for example, in certain instruments designed for use with capillary fill devices for determining coagulation characteristics of blood, the rate of flow of the liquid through the capillary flow conduit is sensed and used as a parameter in the test sequence. In such testing applications the capillary flow conduit not only serves to deliver the fluid to the vented test volume, but it serves as well to provide means for measuring flow characteristics, i.e., viscosity, of the test fluid as it is delivered to the test volume.
Capillary fill test devices clearly offer the advantage of enabling consistent programmed analysis of small uniform sample volumes. However, the inherently small dimensions of such capillary fill devices also complicate their use, particularly for users having impaired vision or dexterity. Proper filling of a capillary fill device requires that an adequate volume of the test fluid be delivered to the fluid receiving portion and be in contact with the capillary aperture of the capillary flow conduit. The design of some commercially available capillary fill devices is such that an adequate volume of test liquid can be delivered to the fluid receiving portion without contacting the capillary aperture and thus without proper filling of the device.
The present invention addresses that problem and facilitates filling of capillary fill test devices. It provides an improved device having test fluid receiving portion communicating with a capillary flow conduit having a capillary aperture which is much enlarged relative to the flow through cross-sectional area of the capillary flow conduit and the flow through cross-sectional area of the fluid test volume. The enlarged capillary aperture facilitates the filling and use of the device essentially by providing a larger, user friendly, target area for delivery of test fluid for filling the device. When the test fluid is blood, the sample is typically delivered to the device by the user as a finger stick sample, a blood droplet that is formed on the finger after a pin stick. There is obvious advantage to ensuring proper loading or filling of the device on the first try.
Thus, in accordance with one embodiment of the invention there is provided a capillary test device having a fluid sample receiving portion, a vented capillary fill test volume having a first flow through cross-sectional area, and a capillary flow conduit extending between the test volume and the sample receiving portion, and having a capillary aperture for contacting a fluid sample delivered to the sample receiving portion. The capillary flow conduit has a predetermined width in plan view and a flow through cross-sectional area that is less than the cross-sectional area of the capillary aperture and less than the maximum flow through the cross-sectional area of the test volume. In one embodiment the device is constructed using plate elements to form opposite walls of the capillary fill test volume and the capillary flow conduit. The plate elements can be spaced apart using a spacer formed to define the fluid receiving portion, the conduit and the test volume, or one of the plate elements can be formed to include capillary channels in its surface which channels cooperate with the second plate element to define the device capillary fill components. The sample receiving portion can be formed as a port in one plate element. The port is sized to have a dimension greater than or equal to the width of the capillary flow conduit. In one embodiment the capillary flow conduit includes an annular capillary portion having an inner edge coincident with the perimeter of the port so that the capillary aperture of the capillary flow conduit has a cross-sectional area equal to the product of the perimeter of the port and the distance between the opposite walls.
In another embodiment of the present invention the capillary fill device is constructed using spaced apart plate elements to form opposite walls of the capillary fill test volume and the capillary flow conduit. The plate elements have first and second opposite ends and first and second opposite lateral edges. The fluid sample receiving portion and the capillary aperture are defined by at least a portion of the edges of the spaced apart plate elements. The edges of the plate elements defining the capillary aperture can be shaped to provide a visibly discernible indication of the location of the sample receiving portion and the capillary aperture.
In still another embodiment of the present invention there is provided a capillary fill test device having a fluid sample receiving portion, a vented capillary fill test volume having a first flow through cross-sectional area, and a capillary flow conduit having a second flow through cross-sectional area less than said first flow through cross-sectional area. The conduit extends between the test volume and the sample receiving portion and has a capillary aperture for contacting a fluid sample delivered to the sample receiving portion. The capillary aperture is sized to have a cross-sectional area greater than the maximum flow through cross-sectional area of the capillary fill test volume. In that embodiment the sample receiving portion can include a fluid delivery port, and the capillary conduit can include an annular capillary portion communicating with the port. The port is preferably sized to have a dimension greater than the width of the capillary conduit.